Many people, in particular office workers, spend a considerable part of their working hours sitting down. Physicians and ergonomics specialists have found that a wrong sitting posture is a primary source of backache complaints and that a person who spends many hours leaning over a table subjects the muscles of his back to considerable strain. For this reason, it is important that the chair is designed correctly and adjustable to satisfy the user's requirements in order to give optimal support to his posterior and back in all sitting postures.
Office chairs normally comprise a seat on a base-mounted central column which is vertically adjustable for setting the seat height, a back-rest which also is vertically adjustabnle and tiltable backwards from a resiliently restraining forward position, and a mounting on the lower side of the seat, by means of which the seat is connected with the central column and the back-rest via a back-rest support secured to the back-rest. The mounting also comprises the operating levers or the like for the different seat and back-rest movements.
To enable optimal adjustment of the seat and the back-rest, the operating levers must be easily operable and readily accessible. Presentday adjustment means often have a stepwise function, which is a disadvantage because they do not permit exact and individual adaptation of the seat and the back-rest to the user's requirements, or at least make such an adaptation more difficult. In addition, the adjusting means sometimes are unnecessarily complicated, which makes the construction more expensive and more susceptible to functional trouble. The arrangement of one operating lever for each seat and back-rest movement is less suitable because this means that the levers must be operated alternately in order to obtain the desired seat and back-rest positions, and as a result the final position frequently will be more or less a compromise.